The present invention relates to a communication system and, more particularly, to a system for transmitting data between a transmitting platform and a receiving platform using leaky coaxial cable as the transmitting antenna located on the tramsmitting platform.
For cross reference purposes, the existence of a concurrently filed application, Ser. No. 07/317,026, is noted. This application, entitled "Communication System For Transmitting Data Between a Transmitting Antenna Utilizing Strip-line Transmission Line And a Receive Antenna in Relative Movement to One Another" by Timothy R. Fox, is commonly owned by the same assignee.
The primary use of such systems employing leaky coaxial cables is for communication in tunnels or in large buildings where portable receivers are used to receive data from a transmitter. A difference between this elementary version of the system and a system for transmitting data between a rotating platform and a stationary platform is that, in the elementary system, the receive antenna is in a far field region and thus picks up the radiated electromagnetic wave from the entire transmitting antenna. In the rotating platform and stationary platform arrangement, the receive antenna is in very close proximity to the transmitting antenna and the receive antenna senses the electromagnetic field from the voltage on the transmission line near the receive point.
A communication system for transmitting data between a rotating platform and a stationary platform finds particular utility in CT scanners. The data come from a transmitter source and are applied to a suitable modulator that modulates a sinusoidal radio-frequency carrier signal. The modulated carrier signal is applied to the feedpoint of the transmitting antenna. The transmitter carrier source, the suitable modulator and the transmitting antenna are mounted on the transmitting platform, and the transmitting platform is rotating.
The transmission often is achieved using brushes sliding against slip rings to make a set of electrical connections beween the rotating and stationary platforms. This mechanical contact causes a number of problems, however. The first problem is that the mechanical interface is highly susceptible to wear. A second problem is that the mechanical interface achieves only intermittent electrical contact.
Thus, a problem with present CT scanners is that a large portion of the equipment rotates, but the data received from the rotating equipment must be communicated to a computer that does not rotate. Aside from the mechanical linkages discussed above, other CT scanners are flexible cables to connect the rotating platform to the fixed platform. As a result, most CT scanners cannot allow the platform to rotate continuously. Thus, the rotating platform will make, for example, two rotations and then the transmitting cable must be rewound and the rotations started over again for another two rotations. This procedure causes wear on, and early destruction of, the cables. Moreover, the scanning procedure is rendered unnecessarily long because the platform cannot continuously rotate.